This invention relates in general to adhesive-backed labels, and more particularly, to labels of the type that use an adhesive with high peel strength and very low shear strength characteristics, such as are attached to the outer surface of a rubber tire.
Manufacturers print labels using xe2x80x9con-demandxe2x80x9d printing technologies, thermal transfer printers, for example, and apply the labels to the products they produce, using automated application equipment. This equipment is commonly called a xe2x80x9cprint and applyxe2x80x9d machine. These printed labels provide information concerning the products as well as warnings. For example, in the tire manufacturing industry, a so-called xe2x80x9ctread labelxe2x80x9d may bear the tire manufacturer""s trademark, the size of the tire, and perhaps a bar code identifying the tire. It may also have a warning relating to procedures for installing the tire on a wheel rim.
The typical label is die-cut from material that has a face sheet and a pressure sensitive adhesive spread over, or applied to, a back surface of the face sheet. The front surface of the face sheet has a print receptive coating on which information is printed or at least is exposed so that information may be printed on it. In most cases, the outer surface of the adhesive on the back surface of the face sheet is attached to a release liner. The release liner is normally formed from paper or film having a silicone or fluorocarbon release agent on one face, and the adhesive side of the face sheet is brought against the coated surface of the release liner. Thus, while the adhesive adheres to the release agent, it does so with less than a firm bond, so that the liner can be easily peeled back from the label.
Typically, the label is die-cut through the face sheet and the adhesive, but not through the liner. The labels lie end to end along the liner with slight spaces between successive labels and spaces between the side edges of the labels and the side edges of the liner. Face sheet and material outside the area of the label, commonly called the xe2x80x9cmatrixxe2x80x9d, is peeled away, leaving the labels attached to the liner with exposed areas of liner surrounding each label. Most commonly, the face sheet and the adhesive extend to all edges of each label. Less commonly, so-called xe2x80x9czone coatedxe2x80x9d adhesives result in labels with face sheet and adhesive extending to the leading and trailing edges only, while the face sheet extends beyond the adhesive on the side edges of each label. The liner with the labels attached to it is wound onto a cardboard or plastic core-holder to form a roll for storage, handling, and mounting on the print and apply machine.
In some industries, these labels must be applied to products made of certain low surface energy materials, or materials that excrete plasticizers and oils, or very coarse materials with deep pores. Examples include plastic containers, tire treads and carpet backing. For those products, typically labels are made with adhesives that flow into the products"" surface pores and are chemically resistant to plasticizers and oils. In the case of labels applied to rubber tires, usually. Usually such an adhesive has a rubber base that enables it to adhere well to the treads of rubber tires and to other surfaces as well, but the rubber also allows the adhesive to flow at ambient temperatures. Adhesive flow at ambient temperature is called xe2x80x9ccold flowxe2x80x9d, and an adhesive exhibiting such characteristics is sometimes hereinafter referred to as a xe2x80x9ccold flow adhesivexe2x80x9d. An undesirable consequence of cold flow is that the adhesive exudes beyond the ends of the labels and becomes exposed on the web in the regions between successive labels. Then, when wound into a roll, the compressive force exerted on the labels of the convolutions, particularly the inner convolutions, intensifies the extrusion of the adhesive beyond the ends of the labels. Some adhesive may also exude from the sides of the labels. As a consequence, the exposed adhesive tends to bond the convolutions together and disrupt withdrawal of the liner and its labels from the roll. Just as detrimental, the exposed adhesive transfers to the rollers of print and apply machines, causing the liner and labels to wrap around the rollers and jam the machine. The exposed adhesive can also coat print heads and disrupt their operation.
In accordance with this invention, generally stated, a label is provided having a face sheet on which information may be printed, and an adhesive with cold flow characteristics, sometimes referred to as a transfer adhesive, along the back of the face sheet. The adhesive is positioned on a liner, and formed, as by die cutting, to closely predetermined dimensions. The peripheral edges of the face sheet are die-cut beyond the edges of the adhesive, producing a margin around the edges of the label so that if the adhesive exudes, it will not flow beyond the edges of the face sheet. The adhesive on the labels adheres to a release agent on the liner, with the labels being arranged one after the other on the liner, thus producing a web of labels. In addition, the present invention includes a process for producing the web. That process includes depositing a strip of transfer adhesive on a liner, die cutting the adhesive strip to produce a succession of adhesive patches with a matrix outside the patches, removing the matrix, placing over the patches and liner an outer strip of material suitable for the face sheets, and die cutting the outer strip beyond the margins of the adhesive patches.
In the preferred embodiment described, a layer of firm adhesive is applied to an undersurface of the outer strip. A film with two broad surfaces is adhered on one broad surface to the transfer adhesive layer before the transfer adhesive is die cut, and die cut with the adhesive, which makes the film coextensive with the patches of transfer adhesive. The other broad surface of the film is adhered to the firm adhesive. The firm adhesive extends beyond the edges of the film into the margin between the face sheet and the adhesive patches. The firm adhesive serves to adhere the edges of the label to the liner and to some extent, to the article to which the label is applied, and to the film. The film serves as reinforcement to the transfer adhesive, which, especially when very thin, tends to be fragile.